Radiation used in radiation tomographic imaging is continuous radiation. Therefore, as the radiation passes through a subject and attenuates, a beam hardening phenomenon occurs, wherein a high-energy portion in a radiation spectrum relatively grows and becomes hard to attenuate. In particular, in a body region including tissue like a bone part that has a higher radiation absorption coefficient, such a beam hardening phenomenon noticeably occurs. Consequently, in a reconstructed image, an effect thereof emerges as beam hardening artifacts.
Thus, when a radiation tomographic image is produced by scanning a body region including a bone part and soft tissue, what is generally called beam-hardening correction is performed for suppressing the beam hardening artifacts.